The polymerization of one or more alpha olefins in a gas phase process using Ziegler-Natta catalysts has been practiced commercially for a long time. The polymers produced are considered to be crystalline and are granular, free-flowing and are non-sticky or "dry".
More recently, the polymerization of ethylene-propylene rubbers (EPRs) such as ethylene-propylene-diene (e.g., ethylidene norbornene, ENB) have been successfully produced commercially in a gas phase process using a vanadium catalyst and an inert particulate material (e.g., carbon black) to maintain the bed of forming polymer in the fluidized state. The so-called "sticky " polymers produced are amorphous, but otherwise granular, free-flowing, and non-sticky or appear "dry".
Only most recently, it has been demonstrated that a third class of polymers can be produced by gas phase polymerization processes. However, these polymers have not as yet been produced commercially using a gas phase process. In these gas phase processes, high cis 1,4-polybutadiene can be produced by the gas phase polymerization of 1,3-butadiene using several catalyst systems, preferably in the presence of an inert particulate material such as carbon black and/or silica. See, for example, U.S. Pat. Nos. 4,994,534 and 5,453,471, as well as WO 96/04322 and WO 96/04323. In these processes significant amounts of liquid monomer (butadiene) are present in these gas phase polymerizations. The polymers produced are highly amorphous, granular, free-flowing, appear "wet" (that is they tend to want to clump together over time under certain conditions and develop characteristics of stickiness).
For the gas phase production of polybutadiene on a commercial scale, start-up and passivation procedures presently employed in the production of alpha olefin homo- and copolymers and EPR/EPDMs have not been effective. Such attempts have resulted in an unusually long induction period, difficulty in achieving reactor process control, wasted catalyst and co-catalyst, and an increase in undesirable side-reactions.
Accordingly, there is a need for an improved start-up and passivation process for the gas phase production of polybutadiene.